KR20230160831A - Aerated biological filtration method for water treatment to reduce nitrogen content (NGL) in water with reduced carbon source and aeration requirements - Google Patents

Abstract

The present invention relates to a method for biological filtration of water loaded with nitrogen pollutants for reducing the overall nitrogen content of the water loaded with nitrogen pollutants, comprising: a first stage of filtration, a second non-aerated biological reactor, and carried out in a first aerated biological reactor. A second stage of deammonification, denitrification and filtration carried out in a biological reactor, and evaluating the ratio of the nitrite content to the ammonia nitrogen content of the water at the outlet of the first reactor. If this ratio is greater than the predetermined stoichiometric value, the process according to the invention obtains, at the inlet of the second reactor, a mixture with a ratio of nitrite content to ammonia nitrogen content close to the stoichiometric ratio of the anammox reaction. To this end, it includes adding water to be treated to the water originating from the first reactor.

Description

Aerated biological filtration method for water treatment to reduce nitrogen content (NGL) in water with reduced carbon source and aeration requirements

The present invention belongs to the field of biological treatment technology of water, especially wastewater, especially industrial and municipal wastewater. More specifically, the present invention relates to the biological treatment of nitrogen loaded water, which is used to adjust the stoichiometry of the anammox reaction before a portion of the water to be treated enters the reactor where the anammox reaction occurs. It's about filtration methods.

Currently, biological wastewater treatment methods are being carried out to reduce the nitrogen pollutant content.

These methods are based on the bacterial communities present in the treatment reactor and the different reaction mechanisms of nitrogen products.

For example, the nitrification-denitrification process is based on the performance of an aerated phase and an anoxic phase, either within the same reactor or each in separate reactors. The supply of oxygen during the aeration stage is supplied by AOB (ammonia oxidizing bacteria), which can convert ammonia nitrogen (NH ₄ ⁺ ) to nitrite (NO ₂ ^- ) and nitrite to nitrate (NO ₃ ^- ). Promotes the development of an autotrophic nitrifying bacterial biomass, composed of NOB ( nitrite oxidising bacteria ) capable of Without aeration, the anoxic phase reduces nitrates to nitrites and then to molecular gaseous nitrogen (dinitrogen, N ₂ ), thanks to the organic carbon contained in the wastewater or derived from external organic carbon sources such as methanol. Promote the development of denitrifying biomass.

Although particularly effective, this method is expensive as it requires the supply of large amounts of oxygen and highly exotic organic carbon sources.

A nitritation process, also called “nitrate shunt”, also exists, in which operating conditions are adjusted in a way to promote the development of AOB biomass at the expense of NOB. This process reduces the oxygen consumption associated with the nitrification-denitrification process.

Finally, there is a nitrification-deammonification process in which specific bacterial populations act in the absence of aeration during deammonification, known as Anammox ( Anaerobic AMMonia Oxidation ). Anammox bacteria are autotrophic bacteria and can convert nitrite and ammonia nitrogen to gaseous nitrogen (N ₂ ) and a small amount of nitrate (about 11%) without the need to add an organic carbon source to the reactor. Therefore, this process can reduce the supply of organic carbon and consequently reduce water treatment costs.

Document US2018257966A1 discloses wastewater treatment including biological filtration tanks, nitrification tanks and anammox tanks. Biological filtration tanks are a pretreatment process for incoming wastewater that performs biological filtration and removes solids and organic matter. The nitrification tank carries out the nitrification process of the wastewater originating from the biological filtration tank, returns a part of the wastewater to the biological filtration tank, and supplies the electron acceptors necessary for the removal of organic matter in the biological filtration tank. Anammox tanks carry out the anaerobic ammonium oxidation process of filtered wastewater from biological filtration tanks and nitrification tanks. However, in real conditions, nitrification tanks can produce nitrate as well as nitrite. These nitrates are not treated in the next step, so at the end of the treatment process the water also contains nitrates.

Document WO2018/009348A1 discloses a wastewater treatment process comprising denitrification using electron donors. Electron donors, especially exogenous carbon sources, are added to a dedicated deammonification reactor containing heterotrophic biomass and anammox bacteria. The amount of electron donor supplied is adjusted according to the amount of nitric oxide measured at the outlet of this reactor. Therefore, an adjustment time is required between the moment of measuring the nitrogen product in water and detecting deviations from the expected value and the moment of restoring the correct deammonification conditions in the reactor after adding the electron donor.

Therefore, a technology that does not require an external supply of carbon or requires a reduced amount compared to existing solutions is needed. In reality, this exotic supply of carbon represents a high cost item in wastewater treatment.

Additionally, techniques are needed to predict deammonification performance degradation to prevent the production of treated water from failing to meet health and/or regulatory requirements during rather long adjustment times.

One object of the present invention is to propose a method for treating nitrogen-loaded water, in conjunction with solutions known from the prior art, in which the consumption of oxygen and/or carbon sources is further reduced.

Another objective is to propose a method for treating nitrogen-loaded water, in which optimization of deammonification conditions is carried out immediately.

Therefore, the object of the present invention is to propose a method for treating nitrogen-loaded water that is more economical and at least as effective as the methods known from the prior art.

These objects, as well as other objects that will become apparent below, are achieved by the present invention.

The present invention proposes a biological filtration method for water loaded with nitrogen contaminants to reduce the global nitrogen content (NGL) of water, with no or little need for external supply of carbon sources. Furthermore, the method according to the invention makes it possible to optimize the deammonification process independently of the nitrogen oxide or ammonia nitrogen value measured at the end of the method according to the invention.

The process according to the invention comprises a first stage of nitrification and filtration and a second stage of deammonification, denitrification and filtration.

The first stage of nitrification and filtration is an autotrophic biomass consisting mainly of AOB with a bed of filter medium (which thereby contains ammonia nitrogen (NH ₄ ⁺ ) in the water to be treated). It consists in passing the water to be treated through a first aerated biological reactor containing nitrite (NO ₂ ^- ), a portion of which is converted to nitrite. Through this first step, filtered water rich in nitrite and low in nitrate (NO ₃ ^- ) can be obtained at the outlet of the first reactor.

The second stage of deammonification, denitrification and filtration passes the nitrite-rich, nitrate-poor water from the first reactor along an ascending flow to a second non-aerated biological reactor. It consists of This non-aerated biological reactor has a first stage containing a moving medium containing a bacterial biomass consisting primarily of anammox and heterotrophic bacteria and a second stage containing a bed of filter media.

During the second stage, another portion of ammonia nitrogen, nitrite from the first reactor and nitrite produced by heterotrophic bacteria are predominantly converted to molecular nitrogen and a small amount of nitrate by anammox bacteria. (Deammonification).

Additionally, during this second stage, nitrate from the first reactor and a small amount of nitrate produced by anammox bacteria are converted to nitrite by heterotrophic bacteria (denitrification).

Moreover, during the second stage, the water originating from the first stage is filtered again in the second stage.

The method according to the invention also includes the step of assessing the ratio of the nitrite content to the ammonia nitrogen content of the water leaving the first reactor.

The method according to the invention is, at the inlet of the second reactor, at the stoichiometric rate of the anammox reaction, when the ratio of the nitrite content to the ammonia nitrogen content of the water discharged from the first reactor is greater than the predetermined stoichiometric value. It further comprises adding the water to be treated to the water coming from the first reactor to obtain a mixture having a ratio of nitrite content to ammoniacal nitrogen content close to that of the ammonia nitrogen content.

The process according to the invention is implemented with an external supply of a reduced or even zero carbon source.

restoring the ratio between the nitrite content and the ammonia nitrogen content at the second reactor inlet close to or equal to the stoichiometric ratio of the anammox reaction by supplying water to be treated containing ammonia nitrogen to the water leaving the first reactor. It is possible. The conditions are then optimal for the deammonifying activity of anammox bacteria.

The addition of water to be treated containing a carbon source to the water leaving the first reactor, due to the presence of suspended particles and soluble organic matter, is necessary for correct activity of the heterotrophic bacteria present in the second reactor for nitrate treatment. It is possible to supply any amount of organic carbon. The suspended particles will be filtered out of the second reactor and the soluble organics will be consumed by the heterotrophic bacteria present in the second reactor and will no longer be present in the treated water when it exits the second reactor. Therefore, ingeniously, the method according to the invention does not require an exogenous supply of carbon, or only requires a supply of said carbon reduced as much as possible, making it possible to create conditions favorable for heterotrophic bacterial activity. do. The method according to the invention is therefore more economical and at least as effective as methods known from the prior art.

According to a particular embodiment, the predetermined stoichiometric value is 1 to 2.5, preferably 1.1 to 2, more preferably 1.2 to 1.5.

Accordingly, the supply of ammoniacal nitrogen from the water to be treated is activated as soon as the stoichiometric values deviate from the stoichiometric ratios of the anammox reaction due to the imbalance in favor of nitrite. The predetermined stoichiometric values allow for variations in the ammonia nitrogen content, which will be maintained at an acceptable level for correct activity of the anammox bacteria and will not negatively affect the correct deammonification performance in the second reactor. makes it possible.

According to one embodiment, the nitrite content of water discharged from the first reactor is measured using a probe disposed at the outlet of the first reactor.

According to one embodiment, the ammonia nitrogen content of the water discharged from the first reactor is measured using a probe disposed at the outlet of the first reactor.

These probes are placed at the outlet of the first reactor so that the nitrogen product content of the water entering the second reactor can be rapidly assessed. The information provided by these probes makes it possible to quickly, almost instantaneously, determine the addition of water to be treated to rebalance the nitrite content with respect to the ammonia nitrogen content of the water entering the second reactor.

According to one embodiment, the method according to the invention further comprises the step of measuring the ammoniacal nitrogen content of the water to be treated using a probe located upstream of the first reactor.

This probe also provides a quick reading of the ammonia nitrogen content of the water to be treated and allows better control of the amount of water to be treated added to the water leaving the first reactor.

According to one embodiment, the autotrophic biomass of the first reactor is immobilized on filter media.

In these conditions, nitrification and filtration occur simultaneously thanks to the filter media and the bacteria present in this media.

According to another embodiment, the first reactor includes a first stage comprising moving media and a second stage comprising a bed of filter media.

Under these conditions, nitrification occurs mainly in the first stage. Naturally, autotrophic biomass develops in the filter media of the second stage as well and nitrification can continue in the second stage. The filter media of the second stage makes it possible to filter the water in the first reactor, regardless of whether bacterial biomass develops on its surface. This solution is advantageous because it can also improve the efficiency of nitrification and can be easily performed in existing plants comprising two reactors in two stages connected in series.

According to a specific embodiment, the filter media of the first reactor and/or the second reactor is a fixed bed of particles with a particle size of 2 to 6 mm and a bulk density of 15 to 100 kg/m ³ .

This particle size makes it possible to store biomass and retain particulate pollution. Then, if the water to be treated is added to the water leaving the first reactor, as it passes through the water to be treated, not only the suspended particles present in the water contained in the second reactor, but also the associated particulate organic matter. Materials can be filtered effectively. The particles in this medium (fixed bed) are less dense than water. Therefore, it is naturally located at the top of the reactor by floating, and it is also possible to wash it through gravity washing.

According to a preferred alternative to this embodiment, the particles of the medium (fixed bed) are made of polystyrene.

This material has the advantage of being economical and highly durable.

According to one embodiment, the moving medium of the second reactor and/or, if applicable, the first reactor, has a density of 900 to 1200 kg/m ³ , preferably 920 to 980 kg/m ³ and of the other moving medium. Includes a surface that is protected from collision with the surface.

These media allow anammox and heterotrophic bacterial biomass to develop despite movement due to upward flow of nitrite-rich, nitrate-poor water. This movement can actually cause collisions between the media, causing parts of the biomass located outside of the surface to be detached from collisions.

According to one embodiment, the water to be treated is passed through a settler before providing the water to the first reactor.

This embodiment makes it possible to remove some of the suspended particles and associated particulate organic matter contained in the water to be treated, which may settle to the bottom of the sedimentation tank.

Justice

In the context of the present invention, “anamox reaction” means a deammonification reaction in which nitrite is converted by anammox bacteria into gaseous nitrogen and small amounts of nitrate in the presence of ammonia nitrogen. Based on material evaluation (Strous et al. 1999), the detailed stoichiometry of this reaction can be written as follows:

NH ₄ ⁺ + 1.32 NO ₂ ^- + 0.066 HCO ₃ ^- + 0.13 H ⁺ ⇒ 1.02 N ₂ + 0.26 NO ₃ ^- + 0.066 CH ₂ O _0.5 N _0.15 + 2.03 H ₂ O (Equation 1)

Therefore, within the meaning of the present invention, “stoichiometric ratio of anammox reaction” means the molar ratio of nitrite content to ammoniacal nitrogen content, which is approximately 1.3, consistent with Equation 1 above. This ratio also corresponds to the mass ratio of nitrite nitrogen to ammonia nitrogen (1.3 mg N-NO ₂ /1 mg N-NH ₄ ).

Within the meaning of the present invention, “stoichiometric value” means the molar ratio of nitrite content to ammoniacal nitrogen content, unless explicitly stated.

The process according to the invention makes it possible to feed ammoniacal nitrogen to the water leaving the first reactor when the stoichiometric values reflect an imbalance of the stoichiometric numbers in favor of nitrite. Therefore, the “predetermined stoichiometric value” according to the invention corresponds to the highest stoichiometric value allowed at the inlet of the second reactor. The result of Equation 1 above is that the optimal stoichiometry value is approximately 1.3. As a result, according to one embodiment, the predetermined stoichiometry value according to the invention is equal to 1.3.

However, the predetermined stoichiometric values can be deviated from these values to cover acceptable variations in nitrite and/or ammonia nitrogen content without significantly affecting the activity of the anammox bacteria present in the second reactor. Accordingly, the predetermined stoichiometric value may be 1 to 2.5, preferably 1.1 to 2, more preferably 1.2 to 1.5. In particular, the predetermined stoichiometric values are approximately 1, approximately 1.1, approximately 1.2, approximately 1.3, approximately 1.4, approximately 1.5, approximately 1.6, approximately 1.7, approximately 1.8, approximately 1.9, approximately 2.0, approximately 2.1, approximately 2.2, approximately 2.3, It may be approximately 2.4 or approximately 2.5.

Within the meaning of the present invention, “external supply of carbon” means the addition of organic compounds, such as methanol, which do not originate directly from the water to be treated and are usually added to promote the activity of heterotrophic bacteria.

“Nitrogen pollutants” within the meaning of the present invention mean derivatives of nitrogen present in waste water.

Figure 1 Figure 1 represents a diagram of a facility suitable for implementing the method according to the invention.
[Figure 2] Figure 2 represents a diagram of another facility suitable for implementing the method according to the invention.
[Figure 3] Figure 3 schematically shows the method according to the present invention.

The inventor emphasizes that it is also possible to improve existing processes for treating water loaded with nitrogen contaminants, in particular to make them more economical. In fact, the inventors have ingeniously shown that it is possible to use water loaded with nitrogen contaminants (the water to be treated) to adjust the nitrite and ammoniacal nitrogen stoichiometry of the anammox reaction before entering the reactor where the anammox reaction takes place. It shows. In addition, waters loaded with nitrogen contaminants contain carbon sources that advantageously make it possible to promote the activity of heterotrophic bacteria responsible for denitrification, limiting or even preventing any external supply of carbon sources. Therefore, thanks to the method according to the invention, oxygen consumption can be reduced by up to 55% and exogenous carbon source consumption by up to 100% in relation to the currently implemented process.

The method according to the invention is a method of biological filtration of water loaded with nitrogen contaminants in order to reduce the total nitrogen content of the water (NGL in the case of N Global).

The method of the present invention will be described in more detail with reference to the drawings for illustrative purposes only, and the purpose of such reference is not to limit the scope of the present invention.

first reactor

The process according to the invention comprises a first stage of nitrification (101) and filtration (102) taking place in a first aerated biological reactor (10) with a bed (12) of filter media. This reactor may comprise known means for injecting oxygen, especially air, such as a ramp located in the lower portion of the first reactor.

Water 100 to be treated is provided to the inlet 13 of the first reactor 10 through the pipe 1 (100a).

According to one embodiment, as schematically shown in Figure 1, water passes through the first reactor 10 in an ascending flow and passes through the autotrophic biomass, consisting mainly of AOB, anchored in a bed 12 of filter media. passes through a filtration and nitrification section containing

In this configuration, nitrification (101) and filtration (102) occur at the same level of the reactor and occur simultaneously. Referring to FIG. 3, water to be treated (100) is led to the inlet (100a) of the first reactor (10), and nitrification (101) and filtration (102) steps are performed simultaneously in the first reactor (10). , there is no need to direct it (101a) from one stage to another in the first reactor.

According to another embodiment, as schematically shown in Figure 2, the water passes in an ascending flow into the first reactor 10 and into the moving medium 11, on which mainly nitrification 101 can be carried out. The autotrophic biomass consisting of AOB is fixed). The water is then directed (101a) to a second stage comprising a filter media bed (12) where the water can be filtered (102). Autotrophic biomass can also develop in the filter media bed of this second stage. In this case, filtration 102 involves nitrification activity.

Generally, first reactor 10 may contain other autotrophic bacteria, such as NOB. However, the conditions inside the first reactor, such as pH, aeration, applied load and/or temperature, in a manner that promotes the development of AOB primarily within the autotrophic biomass, according to techniques known from the prior art. is adjusted to Maintaining low density levels of NOB type bacteria limits the conversion of nitrite to nitrate according to the “nitrate shunt” principle. Therefore, during the first stage, a part of the ammonia nitrogen contained in the water to be treated is converted mainly to nitrite by the AOB. At the end of the first stage, the water obtained from the outlet 14 of the first reactor 10 is rich in nitrite and poor in nitrate.

The first reactor 10 may also contain heterotrophic bacterial biomass that contributes to the reduction (oxidation of dissolved organic carbon to CO ₂ ) of most of the dissolved organic carbon contained in the water to be treated.

It should be noted that heterotrophic and autotrophic bacteria can occur in the bed of filter media (12) and, if applicable, moving media (11) within the first reactor.

The fixed bed 12 of filter particles makes it possible to retain organic matter and suspended particles present in the water during the first step of the process according to the invention.

Nitrite-rich, nitrate-poor water reaches the outlet 14 of the first reactor 10 (102a). The ratio of the nitrite content to the ammoniacal nitrogen content of the water as it leaves the first reactor (10) (14) is then evaluated (103).

second reactor

Water is led (103a) by pipe (2) towards the inlet (23) of the second non-aerated biological reactor (20). The second stage of deammonification, denitrification and filtration of the process according to the invention takes place in the second reactor (20). At the inlet 23 of the second reactor 20, water passes through the second reactor 20 in an upward flow. This passes through a first stage 21 containing a moving medium containing a bacterial biomass consisting of anammox and heterotrophic bacteria. In this first stage (21), deammonification and denitrification occur together thanks to the presence of a carbon source (104). The other part of the ammoniacal nitrogen, the nitrite coming from the first reactor and the nitrite produced by heterotrophic bacteria, is converted by anammox bacteria mainly into molecular nitrogen and a small amount of nitrate (deammonification). At the same time, in the first stage 21, nitrate originating from the first reactor and a small amount of nitrate produced by anammox bacteria are converted to nitrite by heterotrophic bacteria (denitrification). This nitrite is then used by anammox bacteria.

Therefore, the water at the outlet of the first stage 21 mainly contains molecular nitrogen. It then passes to a second stage 22 containing a bed of filter media (104a) where it undergoes a filtration step (105). It should be noted that bacterial biomass may also develop in the filter bed of the second stage, allowing deammonification and denitrification to continue simultaneously with filtration in the second stage.

Media

Preferably, the moving medium of the first reactor and/or the second reactor has a density of 900 to 1200 kg/m ³ , preferably 920 to 980 kg/m ³ and is protected against collisions with the surfaces of other moving media. Includes surfaces that are Such a moving medium is for example the moving medium described in the patent application published as WO2012/136654.

According to a preferred embodiment, the filter media of the first reactor and/or the second reactor consists of a fixed bed of particles with a particle size of 2 to 6 mm and a bulk density of 15 to 100 kg/m ³ . These particles make it possible to retain particulate pollution. Additionally, because it is less dense than water, it is possible to wash particles under gravity. Preferably, these particles are made of polystyrene. According to one variant, these particles are made of expanded polystyrene.

treated water

The water 105a leaving the second reactor 20 is treated water 106. This treated water is led from the outlet 24 of the second reactor 20 by pipe 3. This treated water can be provided for storage, further treatment or distribution depending on its intended use.

Bypass

When the ratio of the nitrite content to the ammonia nitrogen content of the water evaluated (103) at the outlet (14) of the first reactor (10) is greater than the predetermined stoichiometric value (103b), thanks to the so-called bypass pipe (4) Water to be treated (100) is added to the water originating from the first reactor (10) (103c). This makes it possible to obtain at the inlet 23 of the second reactor 20 a mixture with a ratio of nitrite content to ammonia nitrogen content close to the stoichiometric ratio of the anammox reaction.

According to one embodiment, the bypass 4 connects a pipe 1 that provides the water 100 to be treated to the first reactor 10 and directs water from the first reactor 10 to the second reactor 20. It is a pipe connected to the pipe (2) provided by. The bypass (4) may be equipped with a valve (not shown) to control the inflow of water to be treated in pipe (1) and/or a valve (not shown) to control the discharge of water to be treated in pipe (2). You can.

Therefore, in the method according to the invention, the water at the outlet 14 of the first reactor 10 may be different from the water at the inlet 23 of the second reactor 20.

The conditions of the first reactor 10 are adjusted according to known means to ensure efficient conversion of ammonia nitrogen by the biomass primarily to nitrite. These known means are, for example, ammoniacal nitrogen aeration and the load applied in the first reactor 10. Adjustment of the conditions in the first reactor 10 is necessary if the nitrite content of the water becomes too low compared to the ammonia nitrogen content, especially if the ratio of nitrite content to ammonia nitrogen content becomes significantly lower than the predetermined stoichiometric value. need.

As previously indicated, the predetermined stoichiometric value may be 1 to 2.5, preferably 1.1 to 2, more preferably 1.2 to 1.5. In particular, the predetermined stoichiometric values are approximately 1, approximately 1.1, approximately 1.2, approximately 1.3, approximately 1.4, approximately 1.5, approximately 1.6, approximately 1.7, approximately 1.8, approximately 1.9, approximately 2.0, approximately 2.1, approximately 2.2, approximately 2.3, It may be approximately 2.4 or approximately 2.5.

Since the water to be treated 100 contains a carbon source, adding the water to be treated 103c to the water coming from the first reactor 10 also causes heterotrophic bacteria in the first stage 21 of the second reactor 20. It can supply the carbon source necessary for its activity. Accordingly, the process according to the invention is implemented so that the external supply of carbon sources is reduced as much as possible or even zero (O). As shown in the examples, carbon consumption is significantly reduced thanks to the method of the invention compared to known methods. Another advantageous result of the process according to the invention is that the amount of sludge formed by external supply of carbon source is also reduced. However, it may be desirable to supply an exogenous carbon source, for example if the water to be treated does not contain sufficient carbon source to enable satisfactory activity of heterotrophic bacteria. To enable this supply, the second reactor 20 is advantageously provided with a pipe providing the carbon source to the first stage 21 . Carbon source refers to an easily biodegradable carbon substrate such as methanol.

Evaluation of the ratio of nitrite content to ammoniacal nitrogen content (103) is performed from measurements of nitrate and nitrite content. This evaluation can be carried out thanks to known computational devices, for example computational tools carried out by a computer. Such a computer can advantageously control the opening and closing of the valve(s) when present, which may be provided in the bypass 4.

Determination of nitrite content can be performed by any known means. According to one embodiment, the measurement of nitrite content is carried out by means of a probe (31). The use of probe 31 is advantageous because it allows continuous measurement of the nitrite content in water. Such probes are commercially available, for example as the "OPUS" Nitrite probe available from Trios.

Determination of ammoniacal nitrogen content can be performed by any known means. According to one embodiment, the measurement of ammoniacal nitrogen content is carried out by probe 32. The use of a probe is advantageous because it allows continuous measurement of ammonia nitrogen content in water. An example of a probe suitable for measuring ammoniacal nitrogen content according to the invention is the ammonium analyzer sold under the AMTAX brand by Hach.

According to one embodiment, the method according to the invention further comprises measuring the ammonia nitrogen content of the water 100 to be treated. This measurement can be performed by any known means. In certain embodiments, this measurement is performed using a probe 33 located upstream of the first reactor 10, for example in the pipe 1. An example of a probe suitable for measuring ammoniacal nitrogen content according to the invention is the ammonium analyzer sold under the AMTAX brand by Hach.

According to a particular embodiment, the method according to the invention also comprises measuring the nitrate content of the water at the outlet of the first reactor (10). This measurement can be carried out by any known means, especially by a probe (not shown) placed at the outlet of the first reactor, for example in pipe 2. This measurement allows rapid detection of nitrate, allowing the air supply to the first reactor to be reduced to limit NOB type bacterial biomass development.

It is possible to subject the water to be treated to one or more preliminary treatments before providing it to the first reactor 10. In particular, in order to reduce the amount of suspended particles in the water to be treated before entering the first reactor, the method according to the invention may comprise a preliminary step of passing the water to be treated through a settling tank.

Example

Other features and advantages of the invention will become more apparent from the following examples, which are presented for illustrative and non-limiting purposes.

A water treatment plant is arranged to implement the method according to the invention. In particular, a first aerated biological reactor and then a second non-aerated biological reactor are installed and connected by pipes provided with probes for measuring the nitrite and ammonia nitrogen content. The pipe providing the water to be treated to the first reactor is modified in such a way that it also communicates with the bypass pipe. This bypass pipe is connected to a pipe connecting the two reactors to each other upstream of the inlet to the second reactor.

The first aerated biological reactor (10) contains autotrophic biomass consisting primarily of AOB immobilized on filter media (12). It also includes heterotrophic biomass, which can reduce dissolved organic carbon. The second unaerated biological reactor (20) has a first stage comprising a moving medium (21) containing bacterial biomass consisting of anammox bacteria and heterotrophic bacteria, and a filter medium on which the bacterial biomass can also be immobilized. It has a second stage comprising a bed (22).

Water 100 loaded with nitrogen contaminants is provided to the first reactor 10 (100a), and nitrogen aeration and loading conditions in the first reactor 10 are configured in a manner to promote nitrification of ammonia nitrogen. At the outlet 14 of the first reactor, the water is rich in nitrite and low in nitrate. Thanks to probes 31, 32, the nitrite and ammonia nitrogen content of the water is measured at the outlet of the first reactor. The molar ratio of the nitrite content to the ammonia nitrogen content is measured, and if the value of this ratio is greater than 1.7, the water to be treated (100) is injected into the bypass (4) (103c). The water to be treated is mixed with water from the first reactor (10) upstream of the inlet (23) of the second reactor (20), so that the mixture has a nitrite content to ammonia content close to the stoichiometric ratio of the anammox reaction. are mixed to obtain the correct ratio.

Oxygen consumption and carbon source consumption are measured, correlated with the amount of nitrogen treated, and compared to values obtained from existing methods.

References

Strous M, Kuenen JG, Jetten MS. Key physiology of anaerobic ammonium oxidation. Appl Environ Microbiol. 1999 Jul;65(7):3248-50. doi: 10.1128/AEM.65.7.3248-3250.1999. PMID: 10388731; PMCID: PMC91484.

Claims (11)

A method of biological filtration of water loaded with nitrogen contaminants to reduce the total nitrogen content (NGL) of the water loaded with nitrogen contaminants, comprising:
- has a bed of filtration media and contains an autotrophic biomass consisting predominantly of AOB, which allows some of the ammonia nitrogen (NH ₄ ⁺ ) contained in the water to be treated to be converted to nitrite (NO ₂ ^- ). A first stage of nitrification and filtration consisting of passing the water to be treated through a first aerated biological reactor, so that filtered water rich in nitrite and low in nitrate (NO ₃ ^- ) is obtained at the outlet of the first reactor. first step;
- a second stage of deammonification, denitrification and filtration, consisting in passing the nitrite-rich, nitrate-poor water from the first reactor along an upward flow to a second non-aerated biological reactor,
The second unaerated biological reactor is
i) a first stage comprising a moving medium containing a bacterial biomass consisting mainly of anammox bacteria and also heterotrophic bacteria, and
ii) a second stage comprising a bed of filter media,
During this time, another portion of the ammoniacal nitrogen, nitrite from the first reactor and nitrite produced by the heterotrophic bacteria are mainly converted by anammox bacteria into molecular nitrogen and a small amount of nitrate (deammonification),
During this time, the nitrate from the first reactor and the small amount of nitrate produced by anammox bacteria are converted to nitrite by the heterotrophic bacteria (denitrification); and
During which the water originating from the first stage is filtered again in the second stage,
second stage;
- evaluating the ratio of nitrite content to ammonia nitrogen content of the water discharged from the first reactor;
- to obtain, at the inlet of the second reactor, a mixture having a ratio of nitrite content to ammonia nitrogen content close to the stoichiometric ratio of the anammox reaction, if the ratio is greater than a predetermined stoichiometric value, adding water to be treated to the water coming from the reactor
Includes,
Adding water to be treated to the water originating from the first reactor makes it possible to supply the amount of organic carbon required for the correct activity of the heterotrophic bacteria present in the second reactor to treat the nitrate. In addition, a method of biological filtration, characterized in that the method is implemented with an external supply of a reduced or even zero carbon source. A method according to claim 1, wherein the predetermined stoichiometric value is between 1 and 2.5, preferably between 1.1 and 2, more preferably between 1.2 and 1.5. 3. A method according to claim 1 or 2, wherein the nitrite content of the water discharged from the first reactor is measured using a probe disposed at the outlet of the first reactor. Biological filtration according to any one of claims 1 to 3, wherein the ammonia nitrogen content of the water discharged from the first reactor is measured using a probe disposed at the outlet of the first reactor. method. 5. A method according to any one of claims 1 to 4, further comprising measuring the ammonia nitrogen content of the water to be treated using a probe located upstream of the first reactor. . 6. A method according to any one of claims 1 to 5, wherein in the first reactor the autotrophic biomass is immobilized on the filter media. 6. The reactor according to any one of claims 1 to 5, wherein the first reactor comprises i) a first stage comprising a moving medium and ii) a second stage comprising a bed of said filter media. Biological filtration method. 8. The method according to any one of claims 1 to 7, wherein the filter media of the first reactor and/or the second reactor comprises particles having a particle size of 2 mm to 6 mm and a bulk density of 15 to 100 kg/m ³ A biological filtration method characterized by a fixed bed. 9. A method of biological filtration according to claim 8, wherein the particles are made of polystyrene. 10. The method according to any one of claims 1 to 9, wherein the moving medium of the second reactor and/or, if applicable, the first reactor, has a temperature range of 900 kg/m ³ to 1200 kg/m ³ , preferably 920 kg/m 3 . A method of biological filtration, comprising a surface having a density between kg/m ³ and 980 kg/m ³ and being protected from collisions with the surfaces of other moving media. 11. A method according to any one of claims 1 to 10, wherein the water to be treated is passed through a sedimentation tank before being provided to the first reactor.